The present invention relates to a high-quality titanium target for sputtering which is capable of reducing the impurities contained therein, free from the generation of fractures and cracks during high-rate sputtering, capable of stabilizing the sputtering characteristics, and capable of effectively inhibiting the generation of particles during deposition.
The impurity concentration described in the present specification will be displayed in mass percent (mass %) in all cases.
In recent years, various electronic devices have been devised beginning with the exponential advancement of semiconductors, and the improvement of the performance thereof as well as the development of new devices are being sought on a daily basis.
Under these circumstances, there is an inclination toward the miniaturization of electronic devices and equipment and increase in the degree of integration thereof. Various thin films are formed during the manufacturing process of many of such devices and equipment, and titanium, from its unique metallic property, is also used in the formation of thin films of various electronic devices as titanium or titanium alloy films, titanium silicide films, titanium nitride films, or the like.
What is noteworthy upon forming this kind of titanium (including alloy/compound) thin film is that the film itself is demanded of extremely high purity.
The thin films used in semiconductor devices and the like are prone to become even thinner and shorter, and because the distance between the thin films is extremely small and the integration density is increasing, there is a problem in that the substances configuring the thin films or the impurities contained in such thin films become diffused to the adjacent thin films. Consequently, the balance of the constituent substances of the subject film and the adjacent films is disrupted, and there is a major problem in that the functions of the film, which are inherently required, will deteriorate.
During the production process of this kind of thin film, there are cases where the thin film is heated to several hundred degrees, and the temperature also rises during the use of the electronic devices with a semiconductor device built therein. This kind of temperature rise additionally increases the diffusion rate of the foregoing substances, and causes the major problem of deteriorating the functions of the electronic devices due to such diffusion. Moreover, generally speaking, the aforementioned titanium and titanium alloy films, titanium silicide films or titanium nitride films can be formed with a physical deposition method such as sputtering or vacuum deposition. Explained below is the sputtering method which is used most comprehensively among the above.
This sputtering method is a method of physically colliding positive ions such as Ar+ to a target disposed on a cathode and discharging the metal atoms structuring the target with the collision energy thereof. Nitrides can be formed by using titanium or its alloy (TiAl alloy, etc.) as the target and conducting sputtering under a mixed gas atmosphere of argon gas and nitrogen.
When impurities exist in the titanium (including alloy/compound) target upon forming the sputtered film, there are problems in that: the coarsened grains floating within the sputtering chamber become adhered to the substrate and cause disconnection or short circuit in the thin-film circuit; the amount of generated particles, which cause the protrusions of the thin film, will increase; and a uniform film cannot be formed.
In light of the foregoing circumstances, it goes without saying that it was conventionally necessary to reduce transition metals, high melting point metals, alkali metals, alkali rare earth metals or other metals that become impurities, but the current situation is that, even if the foregoing elements are reduced as much as possible, the foregoing particles are still generated, and a fundamental solution has not yet been discovered.
Moreover, while a titanium thin film is sometimes used as a pasting layer for preventing the generation of particles upon forming a titanium nitride Ti—N film, the film is too hard to obtain sufficient strength of adhesive bonding, and there is a problem in that the film becomes separated from the interior wall of the deposition device or components and is unable to function as a pasting layer so that it causes the generation of particles.
In order to improve the production efficiency, there are demands for high-rate sputtering (high-power sputtering). Here, there are cases where the target is subject to fractures or cracks, and these problems tend to prevent stable sputtering. Patent Document 1 and Patent Document 2 listed below are cited as prior art documents.
Generally speaking, in order to improve the sputtering characteristics (uniformity of film thickness, particles), a fine and uniform structure is desirable. With a product having a purity 4N5 (99.995%) or a product having a purity of 5N (99.999%) which is generally used as a titanium sputtering target, an ingot is subject to hot forging, and thereafter cut and subject to rolling and heat treatment in order to obtain a uniform crystal structure having an average crystal grain size of 10 microns or less.
In recent years, materials with higher purity are demanded in cutting-edge processes, and titanium materials are also demanded to have a purity level of 5N5. However, when a high-purity Ti ingot having a purity of 5N5 (99.9995) or higher is used to prepare a target based on the conventional processes and conditions, there is a problem in that a macro pattern irregularity is formed on the target surface, and the average crystal grain size becomes larger than 10 microns. Moreover, upon comparing the average crystal grain size of locations where a macro pattern irregularity is formed and the average crystal grain size of locations where a macro pattern irregularity is not formed, there was a difference of 20% or more.
Consequently, when this target is sputtered, both the uniformity and particles were inferior in comparison to conventional products.
The Prior Art Documents include Patent Documents 3 to 6 related to titanium targets which were previously developed by the Applicant, and other related Patent Documents 7 to 12.
Nevertheless, these Patent Documents mainly relate to the crystal grain size of the titanium target, crystal orientation, and method of bonding the target and the backing plate, and while certain Patent Documents prescribe the purity, the prescribed purity is merely a purity level of 4N5 (99.995%).
None of these Patent Documents investigate the cause of the problems arising when producing a target from titanium having a purity level of 5N5, particularly the deterioration in uniformity and the macro pattern irregularity formed on the target surface that causes the generation of particles, and the problems regarding uniformity and particles still remained.
Patent Document 1: International Publication No. WO 01/038598
Patent Document 2: JP 2001-509548 A
Patent Document 3: JP H07-090560 A
Patent Document 4: JP H07-090561 A
Patent Document 5: JP H07-090562 A
Patent Document 6: JP 2000-204467 A
Patent Document 7: JP H07-278804 A
Patent Document 8: JP H08-333676 A
Patent Document 9: JP H11-050244 A
Patent Document 10: JP 2001-115257 A
Patent Document 11: JP H08-269701 A
Patent Document 12: JP H09-143704 A